//
// Created by Jisam on 2024/7/19.
//
#include <bits/stdc++.h>
#define PSI pair<string,int>
#define PII pair<int,int>
#define VVI vector<vector<int>>
#define VI vector<int>
#define VS vector<string>

#define PQLI priority_queue<int, vector<int>, less<int>>
#define PQGI priority_queue<int, vector<int>, greater<int>>
#define i64 long long

using namespace std;

const int N = 1e5 + 5;
int ans;
void solve() {
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    int maxx = max({a,b,c,d});
    for(int i = 1;i < maxx; i ++){
        if(a == c * i && b == d * i){
            cout << i;
            return;
        }
    }
    cout << "-1";
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
        solve();
    return 0;
}